Vehicle monitoring systems are configured for the purpose of controlling the operations of multiple unmanned dump trucks or the like doing work such as hauling earth and sand over spacious work sites such as at rock crushing or mining facilities, wherein a monitoring station is established as a ground station and the unmanned vehicles are comprehensively controlled and monitored by the monitoring station.
Conventionally, such vehicle monitoring systems have been devised so that transceivers (VHF transceivers, for example) are provided for conducting radio communications between the monitoring station and the plurality of vehicles, various kinds of data including position data for own vehicles measured by each of those vehicles are transmitted to the monitoring station at extremely short intervals (such as every second, for example), whereby the positions of each vehicle can be accurately apprehended in the monitoring station so that collisions, etc., do not occur between the vehicles. The monitoring station that receives the position data, etc., transmitted by the vehicles sends data back to the vehicles to acknowledge receipt of their transmissions, whereby each vehicle can verify any malfunction in the transceiver carried thereby.
In recent years, however, a need has arisen to monitor a greater number of vehicles (50 to 100) in applications where the distances traveled by the vehicles are extremely long (approximately 10 km or so), and where a plurality of travel routes exist. In conjunction with this development, the data volume handled has increased dramatically.
In order to cope with this, it is necessary to provide transceivers of a type capable of performing high-speed radio communication over a wide area (i.e. long-distances).
The following two communication systems are thought to be practical, using current technology, for such vehicle monitoring.
(1) VHF/UHF PA1 (2) SS (spectrum spread system) radio
However, when the VHF/UHF system is employed in the vehicle monitoring system described in the foregoing, although this communication system is capable of communicating over long distances (10 to 20 km) and thus to cover communication over the entire area of a wide work site, the communication speed is slow (9600 bps), resulting in the problem of not being able to continually ascertain the current positions of a plurality of vehicles. That is, such an application involves communicating large volumes of data from the plurality of vehicles to the monitoring station, whereupon the communication data volume becomes large. When this is handled in a communication system wherewith the communication speed is slow, the communication lines become congested, and the load on the communication lines becomes great, to the point where vehicle control and monitoring become truly impossible.
When SS radio ((2) above) is employed in a vehicle monitoring system, moreover, while high-speed communication does indeed become possible (at 256 Kbps), and an extremely large volume of data can be transmitted at high speed, the effective distance of the radio signal is short (100 m to 1 km), so that it is impossible therewith to cover communication over the entire areas of the work sites which are becoming increasingly extensive in area.
Furthermore, in order to cover communication over the entire area of a wide-area work site with SS radio, auxiliary equipment such as radio relay stations must be newly installed in various locations throughout the work site in order to make up for the inadequacy in effective radio signal distance. This results in escalating costs for the initial investment and for maintenance, etc., making practical applications in fact unfeasible.
Thereupon, conventionally, even while employing communication system (1) above, a method has been adopted wherein, in order to augment the vehicle control which the monitoring station is supposed to perform, obstacle sensors are installed in each vehicle so that thereby the presence of other vehicles can be ascertained and collisions avoided. However, collision avoidance systems which depend on such sensors are problematic in terms of safety and so are fundamentally undesirable. This is because of the difficulty in completely avoiding all collisions in cases where multiple vehicles must transit intersections and pass each other from opposite directions.
Furthermore, whether communication system (1) or communication system (2) above is employed, a problem nevertheless remains in that the monitoring station must control all of the vehicles, wherefore the burden placed on the monitoring station becomes excessive.
Thus, conventionally, despite the fact that large volumes of data must be handled, due to problems inherent in the communication scheme of the system, the number of vehicles controllable by the monitoring station has been limited.
In order to resolve these problems, a method has been proposed wherewith vehicle positions are monitored by providing monitoring posts for monitoring the passage of vehicles at various places along the planned travelling path.
However, the installation of auxiliary equipment such as monitoring posts at locations along extensive planned travelling paths involves enormous installation costs, and such measures provide little flexibility for altering a planned travelling path because the positions of the monitoring posts must be changed every time the planned travelling path is altered. Hence this method is problematic in terms of both practicality and convenience.
The present invention was devised in view of the situation described in the foregoing. An object of the present invention is to perform vehicle monitoring wherewith inter-vehicular interference is avoided, without entailing increased costs for deploying auxiliary equipment, and without compromising safety, while minimizing the load on the communication lines and the load on the-monitoring station, and providing high flexibility for making alterations in the planned travelling path.
There have been problems with conventional methods for avoiding vehicular interference at wide-area work sites in that the areas where interference is to be avoided and the form of interference have been limited.
With the "Unmanned Dump Truck Work Area Intrusion Interlock Method and System Therefor" disclosed in Japanese Patent Application Laid-Open No. 198134/1997, for example, the places where interference can be avoided are limited to work areas such as loading sites. Accordingly, as based on this technology, inter-vehicular interference cannot be prevented throughout the entire planned travelling paths over which the vehicles must travel.
The technology disclosed in the patent application cited above, moreover, has in view a particular form, that is, the avoidance of interference that occurs when multiple dump trucks make simultaneous incursions.
In large-scale sites such as mining facilities, however, the forms of interference which can occur are various. Interference (collisions) can occur, for example, where multiple vehicles enter an intersection or loading area at the same time, or where there are multiple vehicles traveling in the same direction on the same travel route at different speeds. At sites such as mining facilities, in particular, the weight of the vehicles differs depending on the volume of earth loaded, whereupon the inter-vehicle speed difference often becomes large, making it critically necessary to avoid interference (collisions) caused by the inter-vehicle speed differences.
Another object of the present invention, which was devised in view of the situation described above, in addition to the object stated earlier, is to make it possible to deal with various forms of interference that can occur over the entirety of the planned travelling paths.